The invention relates to a method for transmitting call-related data, i.e. a call parameter, between switching centres. Additionally, the invention relates to a switching centre and an intelligent network service control point to support the function in question. The transmission of the mobile station identifier of the subscriber initiating the call, i.e. the A subscriber, to a first switching centre in the home network, when the A subscriber roams in a visited network, is described as a primary example of such a technique.
With reference to FIG. 1, in mobile systems, for instance in the GSM system, a technique is used whereby the number of the A subscriber is transmitted to the terminal of the B subscriber during call set-up. The B subscriber can decide on the basis of the number, whether s/he answers the call or not. The mobile station can improve this function by converting the number of the A subscriber into a name, if the name and number combination in question is stored in the memory of the mobile station.
A problem with the arrangement described above is, for instance, that when the A subscriber roams in the area of a visited network NW2, the number of the A subscriber is usually not shown to the B subscriber in the home network NW1, or at least this requires separate agreements between the operators. A concurrent problem is that the A subscriber roaming in the visited network NW2 cannot without separate authentication (identification) listen to the messages accumulated in his/her voice mail box, because the identifier of the A subscriber is not transmitted during call set-up from the visited network NW2 to the home network NW1. Another concurrent problem is that a subscriber roaming in a visited network cannot use number translation services, such as the private numbering service (PNS) or short number service. Within the scope of this application, B subscriber can refer to either an actual subscriber/terminal or a service, such as listening to a voice mail box.
Thus, it is an object of the invention to develop a method and an apparatus implementing the method for transmitting the identifier (such as a number or name) of the A subscriber to the switching centre serving the B subscriber in the home network or to a switching centre providing the corresponding service, independent of any separate agreements between operators. The object of the invention is achieved by a method and an apparatus characterized by what is disclosed in the independent claims. Preferred embodiments of the invention are set forth in the dependent claims.
A simple solution would be to define a standard according to which the identifier of the A subscriber must also be transmitted in the a set-up message between the networks or operators.
In spite of its apparent simplicity, this approach has, however, proved to be astonishingly difficult, maybe because several operators have made separate agreements that differ from each other and the operators are reluctant to lay them aside for the good of a common standard.
The invention is based on the idea that call set-up is supplemented by means of intelligent network technology. The switching centre of the home network NW1 is referred to as the first switching centre and the switching centre in the visited network NW2 as the second switching centre. In a network element of an intelligent network, for instance a separate service control point SCP, an intelligent network service is located, which instructs said network element, in response to an intelligent network service initiation message received from a second switching centre, to save into its memory the A subscriber identifier (more generally: the data which should be transmitted to the first switching centre, but which according to prior art are not transmitted from one network to another), to allocate to the call in question an identifier, with which the saved data can later be found, and to transmit the identifier to the second switching centre. The identifier is preferably in the format of a telephone number and it is referred to as a homing number. The second switching centre transmits said identifier, i.e. homing number, to the first switching centre which, on the basis of it, retrieves the necessary data, such as the identifier of the A subscriber, from the service control point. The first switching centre can, as necessary, transmit the identifier of the A subscriber to a possible B subscriber or use it to implement the service, for instance to unload the voice mail box of the A subscriber.
The invention provides the advantage that the identifier of the A subscriber is not transmitted from a visited network to the home network in the call set-up message, but using intelligent network signalling, for instance in an intelligent network service initiation message. Intelligent network messages between networks are defined within the CAMEL (Common Applications for Mobile Enhanced Logic) protocol. Correspondingly, intelligent network messages inside networks are defined within the INAP (Intelligent Network Application Part) protocol. These protocols are sufficiently well standardised, which means that the network elements supporting them also support the transmission according to the invention of the A subscriber identifier between a visited network and the home network. The operators will thus not need several separate agreements differing from each other.